The present invention relates generally to earth boring apparatus and more specifically to a device for interconnecting an earth boring hammer provided with an expander cone together with a drag or follower pipe.
Devices of the type to which the present invention relates have been utilized to produce trial borings, land ties and ground injections whereby the ground or earth is displaced by an earth displacement boring hammer with the borings thus produced being propped or stabilized by follower or drag pipes which are moved into the boring behind the earth displacement hammer and which support the earth surrounding the boring. Lateral displacement of the earth within which the boring is to be made is effected specifically by an expander cone which follows the hammer into the boring. The expander cone is normally located about the boring hammer and is dragged therewith into the boring. Normally, the expander cone is prevented from moving rearwardly of the hammer beyond a specific degree by means of an engagement which is provided between the cone and the hammer so that as the hammer moves downwardly it may abut a shoulder or other structural part of the cone and move the cone therewith into the boring. Thus, the expander cone will normally operate as a collar about the hammer.
The rear end of the expander cone may be connected, for example, with the follower or drag pipe which may consist of steel or plastic material. Since the inside diameter of the drag pipe is greater than the diameter or collar of the earth displacement hammer serving to prop the expander cone, the displacement or boring hammer may be withdrawn through the drag pipe after a predetermined stage of the boring operation so that the drag pipe may be subsequently utilized for further introduction of materials into the boring or may also be withdrawn from the boring.
Generally, a plurality of drag pipes may be connected to the initial drag pipe which is attached to the displacement hammer. In the event that the load of the plurality of drag pipes being inserted into the bore becomes too heavy or if the friction between the drag pipes and the surrounding earth becomes great, the displacement hammer may no longer be capable of pulling or dragging the expander cone and the drag pipes into the boring. In the event that this occurs, it is generally necessary to apply to the outer end of the drag pipes a force, in addition to the force applied to the boring hammer, in order to drive the drag pipes and the expander cone into the boring. Generally, it has been the procedure to apply such a force by means of a hydraulic press having a hollow piston and self-gripping tongs.
Although by this method the drag pipes and the expander cone are driven into the boring in a generally satisfactory manner, in order to overcome excessive friction between the drag pipes and the earth, this type of procedure for driving the apparatus into the ground gives rise to certain disadvantages inasmuch as the boring hammer itself is usually not firmly supported toward the rear at the point where a connection is made with the leading drag pipe. This usually is necessary and advantageous in order to achieve an optimum percussive effect upon the boring hammer. The support in the drag pipe is not available inasmuch as there must be no projecting stop means or other similar devices so as to avoid that the collar of the displacement or boring hammer would strike against such a stop when the hammer is retracted otherwise it could no longer be brought rearwardly of the boring.
Thus, the object of the invention is to provide a device for suitably connecting a boring or earth displacement hammer operating with an expander cone with the drag or follower pipes which must be utilized, the device operating to insure with a simple and uncomplicated structural arrangement the automatic connection and disconnection between the boring hammer and the drag pipe while at the same time operating to support the boring hammer toward the rear thereof.